1. Field of the Invention
The present invention relates to an organic electro-luminescent (EL) display device, and more particularly to a top-emission-type organic EL display device which can enhance the uniformity of brightness and can enhance the reliability of the organic EL display device.
2. Description of the Related Art
An organic EL display device is classified into a bottom-emission-type organic EL display device in which light emitted from organic EL layers is taken out in the direction of a glass substrate on which the organic EL layers and the like are formed and a top-emission-type organic EL display device in which light emitted from organic EL layers is taken out in the direction opposite to a glass substrate on which the organic EL layers and the like are formed. The top-emission-type organic EL display device has an advantage that the respective organic EL layers can ensure a large area thus increasing the brightness of a display.
In the organic EL display device, the organic EL layer is sandwiched between a lower electrode and an upper electrode, and emission of light from the organic EL layer is controlled by applying a fixed voltage to the upper electrode and by applying a data signal voltage to the lower electrode thus forming an image. The supply of the data signal voltage to the lower electrode is performed via a thin film transistor (TFT). In the top-emission-type organic EL display device, it is also possible to form the organic EL layer on the TFT and the like and hence, a light emission area of the display can be increased.
The top-emission-type organic EL display device radiates light toward the upper electrode side and hence, it is necessary to make the upper electrode transparent. As a transparent electrode, an ITO (Indium Tin Oxide) film, an IZO (Indium Zinc Oxide) film or the like which is a metallic oxide conductive film is used in general. However, ITO, IZO or the like exhibits high resistance compared to metal. Accordingly, when a distance between the upper electrode and a terminal portion which supplies an electric current to the upper electrode is increased, a potential of the upper electrode arranged in the vicinity of the terminal portion and a potential of the upper electrode remote from the terminal portion differ from each other. This difference appears as the non-uniformity of brightness thus deteriorating an image quality.
JP-A-2002-318556 (patent document 1) and JP-A-2001-230086 (patent document 2) disclose a top-emission-type organic EL display device in which an auxiliary electrode is provided for suppressing a phenomenon that a potential of an upper electrode differs depending on a position of the upper electrode due to resistance of the upper electrode.